Dihydrofolate reductase (DHFR) gene amplification mutants will be used as model systems to identify and characterize a transcription unit whch gives rise to at least seven discrete mRNAs. A major effort will be devoted to the functional analysis of RNA polymerase II transcription termination sites. Proposed research will also identify and characterize additional trancription units or other genetic information, located in the vicinity of the DHFR gene. Such information should result in a better understanding of genome organization and the regulation of gene expression in mammalian cells. Proposed experiments are centered around the three topics listed below and will be designed to answer the specific questions listed under each topic. I. Identification and characterization of the DHFR transcription termination site. 1. Where is the DHFR transcription termination site located? 2. Does transcription termination occur at a unique site? 3. What are the DNA sequence requirements for a functional transcription termination site? II. The use of modular transcription units to study mRNA metabolism. 1. Does transcription termination play a role in gene expression? 2. What is the fate of a transcript that lacks a polyA tail? 3. What is the fate of a transcript that lacks a 5' cap structure? III. Structural and functional analysis of a transcription unit located in front of the DHFR gene. 1. What are the boundaries of this transcription unit? 2. What is the functional relationship between DHFR and this adjacent transcription unit?